Due to miniaturization of semiconductor devices, a haze (defect) on a reticle generated in a lithographic process has been a major issue. The haze on the reticle is said to be caused when nuclei agglutinate due to exposure energy, the nuclei being formed by a chemical reaction between an acid and a base present in the surface of the reticle or present in atmosphere or formed by a photochemical reaction of organic impurities. The haze on the reticle is increased in size by, e.g., the photochemical reaction whenever exposure is repeated, and finally grows into a size in which the haze may be regarded as a defect on a wafer. Therefore, the haze is called a growing defect (hereinafter briefly referred to as “GD”). Recently, due to the miniaturization of semiconductor devices, resolution has been improved by a reduced wavelength of a light source of an exposure apparatus. Accordingly, light energy provided for the photochemical reaction has been increased, and the growth rate of the defect has been further rising. For example, in exposure using a light source of KrF (wavelength: 248 nm), the GD affects about 5% of the reticle. On the other hand, in exposure using a light source of ArF (wavelength: 193 nm), the GD affects 20% of the whole reticle. This is the cause of a decreased yield.
As countermeasures, ammonium sulfate which is one of the causative substances is removed from the exposure apparatus through a filter in an attempt to inhibit the generation of the GD. However, in the present situation, the generation of the GD is not prevented completely. While the generated GD can be partly removed by cleaning the reticle, this cleaning process not only requires the cleaning of the reticle but also requires the removal of a pellicle and the attachment of a new pellicle after the cleaning. This leads to additional costs. Moreover, if cycles of cleaning the reticle are increased to reduce the GD, a phase shift, reticle transmittance and a mask CD value change whenever cleaning is repeated. Disadvantageously, this results in a reduced life of the reticle and a significant rise in costs. Therefore, at the present time, the generated GD has to be detected before a device yield is severely affected. As a result, the reticle has to be frequently inspected, leading to a problem of decreased productivity.
As is already known, not all the defects detected on the reticle are transferred onto the wafer and form defects. For example, in the manufacture of a semiconductor device, defects transferred onto the wafer are only regarded as important. Accordingly, one method to enable an inspection that takes into account the defect transferring tendency of the reticle is to simulate an exposure optical system by a computer, thereby to create actual wafer images with respect to images of transmitted light and reflected light of the reticle, and to detect defects in the wafer images. However, a unit that carries out this method has to be provided with an optical system equivalent to that of the exposure apparatus and thus leads to a higher hardware price. Consequently, there is a problem of significantly increased inspection costs in the case of frequent inspections for monitoring the growth of a defect such as the GD. Furthermore, a current GD inspection is intended to detect defects generated on an L/S (Line and Space) pattern, and therefore uses, for example, an inspection specification stipulating that a representative CD value of a defect be 10% or less of a design CD. However, in the case of a GD generated on a complex pattern shape of, for example, a peripheral portion, it is difficult to define a representative CD value, and the above-mentioned inspection specification is meaningless.